1. Technical Field
The present invention relates to a chip-shaped electronic component to be used in various electronics. More specifically, it relates to a minute chip-shaped electronic component.
2. Background Art
In an increasing demand for lighter, thinner, smaller electronic equipment, an extremely small sized chip-shaped electronic component has come to be widely used for electronic equipment in order to increase the wiring density of the circuit substrate. Recently, a very small sized chip-shaped electronic component having a length of 1.0 mm, a width of 0.5 mm, and a thickness of 0.25 mm is coming in a main stream.
A conventional chip-shaped electronic component will be described exemplifying a rectangular chip resistor.
FIG. 3 is a perspective view illustrating a configuration of the conventional rectangular chip resistor; and FIG. 4 is a cross sectional view of the rectangular chip resistor of FIG. 3.
In FIGS. 3 and 4, 1 denotes a substrate made of a 96 alumina substrate; and 2 denotes a pair of upper surface electrode layers formed on both ends of an upper surface of the substrate 1. The pair of upper surface electrode layers 2 is made of a thick silver-based film electrode. 3 denotes a resistor layer formed so as to be electrically connected to the pair of the upper surface electrode layers 2. The resistor layer 3 is made of a thick ruthenium-based film resistor. 4 denotes a protection layer formed so as to cover the resistor layer 3 in its entirety. The protection layer 4 comprises an epoxy based resin. 5 denotes a pair of end face electrode layers provided on both end faces of the substrate 1 so that they are electrically connected to the pair of upper surface electrode layers 2. The pair of end face electrode layers 5 comprises a mixed material containing conductive particles and a resin. 6 denotes nickel-plated layers provided so as to cover exposed portions of the end face electrode layers 5 and the upper surface electrode layers 2, and 7 denotes solder- or tin-plated layers provided so as to cover the nickel-plated layers 6. A combination of the nickel plated layer 6 and the solder- or tin-plated layer 7 forms an external electrode.
For example, Japanese Unexamined Patent Publication (Kokai) No. 07-283004 is known as a related art in a field of the invention in the present application.
In the case where a chip-shaped electronic component represented by the above-described rectangular chip resistor is mounted on a glass epoxy board or the like, the chip-shaped electronic component is subjected to a temperature environment of about 250° C. for several seconds in order to melt a solder. In this case, in the above-described chip-shaped electronic component represented by the rectangular chip resistor, such drawbacks occurred that the nickel-plated layers 6 and the solder- or tin-plated layers 7 formed on the end face electrode layers 5 comprising the mixed material containing the conductive particles and the resin are perforated or the solder splashes. In accordance with the recent high density mounting of electronic components, since mounting intervals between the chip-shaped electronic components become narrower, poor conduction and the like due to the above-described drawbacks come to frequently occur.
The inventors in the present application have studied in order to resolve the above drawbacks. As a result of the studies, it was found that the drawbacks of occurrence of perforation in the nickel-plated layers 6 and the solder- or tin-plated layers 7, and the solder splash are adversely affected by a gas generated from the end face electrode layers 5. It is considered that the gas is generated because of remaining moisture, cracked gas and so on. However, it is difficult to specify the cause of the drawbacks and it is considered that a plurality of factors is mixed to cause the drawbacks.